Prostheses which are used to restore dilation or repair otherwise damaged body lumens (such as blood vessels) are known. Typically these prostheses comprise a tubular graft comprised of woven or molded polymeric material, optionally supported in whole or in part by an interiorly or exteriorly disposed mechanical support structure usually referred to as a stent. Prostheses used for this purpose may be introduced percutaneously at an access location remote from a location in a body lumen where the prosthesis is needed but in endoluminal communication therewith. For this purpose, the prosthesis is compressed and held in the compressed state until it has been moved endoluminally to the site in need of repair, where it is expanded and secured. Expansion may be effected, either mechanically by means such as a balloon catheter, or automatically under an elastic or phase change force.
Typically, the prosthesis is retained, in its first configuration, in an outer sleeve or sheath, which may be retained in, or may actually be the forward end of, a delivery catheter. Such a delivery catheter is introduced at the access location and maneuvered through the luminal system to the site where the prosthesis is needed. When the prosthesis reaches that location, it must either be ejected from the delivery catheter, or held in place, while the delivery and/or any surrounding sleeve is retracted.
Another method comprises compressing the prosthesis to a reduced cross-section and then pushing it, in the compressed state, into a catheter which has been previously inserted into the patient. A pusher is used to push the compressed endoprosthesis through the catheter and out the distal end where it expands into place. One drawback of this method is that considerable force must be exerted on the device as it is pushed through the catheter to overcome frictional forces along the lumen. In each of these cases, the cross section of the prosthesis and surrounding catheter, by which it is transported to the deployment location, is a factor which contributes to difficulties in use and deployment of such systems.
In one particular application of such prostheses, an abdominal aortic aneurysm is treated. Such an aneurysm usually occurs in the infrarenal portion of an arterioscleroticly diseased aorta, between the renal arteries and the two iliac arteries, sometimes extending across the aortic bifurcation into one or both iliacs. Typical prostheses for the repair of this region include bifurcated tubular grafts or stent grafts having an aortic section, (typically a section of the prosthesis adapted to be disposed within the aneurysm) and two iliac sections which extend from the aortic section into the iliac arteries. Methods are known which include inserting a bifurcated graft prosthesis endoluminally through one iliac artery and securing it to the aorta by expansion of a stent which is a part of the prosthesis.
It is also known to compress a self-expanding tubular stent-graft and restrain it against a self-expansion force in its reduced cross section configuration, relative to its expanded state, by a knitted strippable sheath. After the sheathed prosthesis is inserted into place within the body, a filament of the sheath is pulled distally to de-knit the sheath and permit its removal as a single filament strand from the prosthesis, allowing the prosthesis to expand to a cross section corresponding to its in-use position. Known sheaths include meshworks of crocheted material extending over the entire length of the prosthesis. One drawback of such an arrangement, however, is that once the drawstring is pulled, expansion of the supporting stent prevents further adjustments of the position of the prosthesis relative to the surrounding lumen.